1. Field of the Invention
The present invention relates to a control system of an internal combustion engine.
2. Background Art
An internal combustion engine is provided with a fuel injection control system which performs calculation of an appropriate fuel injection quantity according to an operation status, and, based on a result of the calculation, drives an injector for injecting fuel. This injector performs opening and closing of a valve constituting the injector by magnetic force generated by applying a current to a built-in coil so that the injector can keep an opened state and a closed state, and performs injection of fuel according to the valve-open period. An amount of injected fuel is determined mainly by a differential pressure between a fuel pressure and an atmosphere pressure of the nozzle hole part of the injector, and a time period during which the valve is kept in the open state to inject fuel. Accordingly, in order to perform fuel injection of an appropriate amount, it is necessary to set a time period during which the valve open state of the injector is kept according to a fuel pressure and perform the open and close operation of the valve quickly and accurately.
Also, in fuel injection to the internal combustion engine, although it is general to perform injection once per time of combustion, it is known that, by injecting a required amount of fuel injection in a manner dividing it into small amounts of fuel and performing injection for several times, homogeneous mixture formation and mixture formation with atomized fuel can be realized in formation of an air-fuel mixture in a combustion chamber, resulting in improvement of stability of an idling operation and purification of exhaust gas as well as improvement of output power. FIG. 19 indicates an example of this relation. As shown, along with increase of the number of times of fuel injection: atomization of injected fuel from an injector is facilitated; homogeneity of the air-fuel mixture in the combustion chamber is improved; and operation performance and output power of an idling operation is improved by improvement of combustion performance of an internal combustion engine, resulting in suppression of soot from the internal combustion engine.
As above, along with demand for performance improvement of an internal combustion engine, an injector and a fuel injection control system capable of small-amount fuel injection is being desired. However, when performing small-amount fuel injection, because it is necessary to shorten a time period to keep an valve-open state of an injector, the proportion of a time period during which a valve transfers from a valve-close state to a valve-open state and a time period during which it transfers from the valve-open state to the valve-close state (invalid pulse) to this valve-open keeping time becomes large, and, as a result, an error of this invalid pulse exercises a large impact directly on the accuracy of an amount of fuel injection. Therefore, in order to perform fuel injection accurately when injecting fuel for a plurality of times in a dividing manner, the following method that improves accuracy of invalid pulse control of an injector is known.
In JP Patent Publication (Kokai) No. 2006-125371A, as a method to improve accuracy of invalid pulse control, there is disclosed a method that, while performing control to increase a fuel injection pulse width gradually from a sufficiently small fuel injection pulse width with which no fuel is injected, detects a change in a fuel pressure measurement value of a common rail, and identifies a fuel injection pulse width from which fuel injection is started actually.
In JP Patent Publication (Kokai) No. 6-257497A (1994), there is disclosed a method that, when controlling fuel injection in a manner being divided into a plurality of times of injection, stops such multi-time injection and controls as a single injection, and learns an invalid pulse of an injector by a difference in an air-fuel ratio at the time of performing the single injection and an air-fuel ratio at the time of performing the multiple-times injection.
However, in the method disclosed in JP Patent Publication (Kokai) No. 2006-125371A, although, as information related to an invalid pulse of an injector, a position with which an injector transfers to a valve-open state from a valve-close state in the operation status in question can be identified, influence of valve close of the injector or a difference in fuel pressures applied to the injector cannot be determined.
Also, in the method disclosed in JP Patent Publication (Kokai) No. 6-257497A (1994), although, by switching to a single injection when performing divided fuel injection using an injector, invalid pulse related information of the injector can be learned, there is a problem that the performance improvement of an internal combustion engine realized by injecting fuel for a plurality of times in a dividing manner is disturbed.
The present invention is made in view of the above problems, and its object is to provide an internal combustion engine control system capable of controlling a fuel injection quantity accurately without disturbing performance improvement of an internal combustion engine.